Preparation process of heat-resistant polymers from polycarboxcylic acids and anhydrides in the presence of an alkali metal fluoride

ABSTRACT

Disclosed herein is a process for preparing heat-resistant polymers by reacting an organic polyisocyanate with one or more compounds selected from the group consisting of organic polycarboxylic acids and organic polycarboxylic acid anhydrides in the presence of an alkali metal fluoride or an alkali metal fluoride combined with a quaternary onium salt as a catalyst.

FIELD OF THE INVENTION

This invention relates to a preparation process of heat resistantpolymers from an organic polyisocyanate and an organic polycarboxylicacid or polycarboxylic acid anhydride.

These polymers are excellent in heat insulating properties, radiationresistance, thermal dimensional stability, mechanical properties,electrical properties, chemical resistance, flame retardancy as well asin heat resistance. They can thus find a wide variety of applications inhigh performance industrial materials such as various industrialmaterials, radiation shield, composite materials, reinforcing materialsand electrical insulating materials. They can be used further as moldarticles, films, papers, fibers, vanishes, adhesives and the like in thefield of electrical and electronic appliances, automobile, vehicles,aircraft, apparel and interior-finishing materials.

DESCRIPTION OF THE PRIOR ART

It has been well known to prepare heat resistant polymers by reactingorganic polyisocyanates with organic polycarboxylic acids or organicpolycarboxylic acid anhydrides. However, it has generally been difficultto obtain polymers of such high molecular weights as to exhibitsufficient properties for forming the polymers into fibers, films,molded articles and the like. Therefore, most of the applications of theresulting polymers have been limited to those as adhesives, varnishesand similar materials. Further, the process involved such problems thatpolyisocyanates used in the reaction gave rise to various side reactionsparticularly at high temperatures upon reaction, thereby causing afrequent formation of gels during the reaction or deteriorating the heatresistance and other properties of the resulting polymers due to thecontamination of by-products into the polymers. Accordingly, a varietyof catalysts have been developed for use in the aforesaid reactionsystem. By way of example, there may be mentioned (1) processes makinguse of metal alkoxides and metal phenoxides (U.S. Pat. Nos. 4,001,186,4,061,611 and 4,061,623), (2) processes in which lactamates are used(U.S. Pat. Nos. 4,021,412, 4,094,864 and 4,094,866), (3) a processrelying upon cyclic phosphorus oxides (U.S. Pat. No. 4,156,065), (4) aprocess in which alkali metal salts of polycarboxylic acids are used(Japanese Patent Laid-Open No. 151615/1982), (5) a process making use ofalkali metal carbonates or hydrogencarbonates (Japanese Patent Laid-OpenNo. 18629/1983), a process in which alkali metal hydroxides are used(Japanese Patent Laid-Open No. 67723/1983), and the like.

In spite of the use of the foregoing catalysts, however, theabove-described processes are accompanied by such drawbacks that theirreaction systems are liable, for example, to form gels frequently or todeposit polymerized isocyanates due to the side reactions ofpolyisocyanates. It has therefore been difficult to obtain linearhigh-molecular polymers and hence to obtain polymers of adequateproperties.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process for thepreparation of linear high-molecular polymers, in the practice of whichno gels are formed during the reaction and the side-reactions due toorganic polyisocyanates are prevented.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have investigated into processes for thepreparation of heat-resistant polymers by reacting organicpolyisocyanates with organic polycarboxylic acids or organicpolycarboxylic acid anhydrides, leading to completion of the presentinvention.

The present invention provides a process for the preparation of a heatresistant polymer which comprises reacting an organic polyisocyanatewith one or more compounds selected from the group consisting of organicpolycarboxylic acids or organic polycarboxylic acid anhydrides in thepresence of an alkali metal fluoride or an alkali metal fluoridecombined with a quaternary onium salt as a catalyst.

Any organic polyisocyanates known per se in the art may be used as theorganic polyisocyanate useful in the practice of the process of thepresent invention. In particular, however, below-described ones may beexemplified. As diisocyanates may be mentioned those described inJapanese Patent Laid-Open No. 151615/1982, for instance,1,2-diisocyanate ethane, cyclohexane-1,4-diisocyanate,4,4'-methylenebis(cyclohexylisocyanate), m-xylenediisocyanate,phenylene-1,4-diisocyanate, phenylene-1,3-diisocyanate,tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate,diphenylmethane-4,4'-diisocyanate, diphenylether-4,4-diisocyanate and1,5-naphthalene-diisocyanate.

As the organic polycarboxylic acid or organic polycarboxylic acidanhydride useful in the practice of the process of the present inventionmay be exemplified below-described ones. Illustrative examples of theorganic polycarboxylic acid may include those described in JapanesePatent Laid-Open No. 179223/1982 as follows; as dicarboxylic acids, forexample, oxalic acid, malonic acid, succinic acid, glutaric acid, adipicacid, pimelic acid, suberic acid, azelaic acid, sebacic acid,telephthalic acid, isophthalic acid, hexahydrotelephthalic acid,diphenylsulfone-4,4'-dicarboxylic acid, biphenyl-4,4'-dicarboxylic acid,thiophene-2,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid,naphthalene-2,6-dicarboxylic acid, 4,4'-diphenylmethane-bis-trimelliticimide acid and 4,4'-diphenylether-bis-trimellitic imide acid; astricarboxylic acids, for example, butane-1,2,4-tircarboxylic acid,cyclohexane-1,2,3-tricarboxylic acid,cyclopnetadienyl-3,4,4'-tricarboxylic acid,cyclopentadienyl-1,2,4-tricarboxylic acid, benzene-1,2,4-tricarboxylicacid, naphthalene-1,4,5-tricarboxylic acid,biphenyl-3,4,4'-tricarboxylic acid, diphenylsulfone-3,4,3'-tricarboxylicacid, diphenylether-3,4,3'-tricarboxylic acid andbenzophenone-3,4,4'-tricarboxylic acid; as tetracarboxylic acid, forexample, butane-1,2,3,4-tetracarboxylic acid,pentane-1,2,4,5-tetracarboxylic acid,cyclohexane-1,2,3,4-tetracarboxylic acid,benzene-1,2,4,5-tetracarboxylic acid,naphthalene-2,3,6,7-tetracarboxylic acid,biphenyl-3,3',4,4'-tetracarboxylic acid,benzophenone-3,3',4,4'-tetracarboxylic acid,diphenylether-3,3',4,4'-tetracarboxylic acid,diphenylsulfone-3,3',4,4'-tetracarboxylic acid,2,2-bis(3,4-dicarboxyphenyl)propane, furan-2,3,4,5-tetracarboxylic acidand pyridine-2,3,5,6-tetracarboxylic acid.

As the organic polycarboxylic acid anhydride may be mentioned, forexample, acid anhydrides derived from tricarboxylic acids, whichindividually contain one carboxyl group and one acid anhydride group inthe molecule, and acid anhydrides derived from tetracarboxylic acids,which individually contain two acid anhydride groups or one acidanhydride group and two carboxyl groups in the molecule. Exemplarypolycarboxylic acid anhydrides may include trimellitic acid anhydride,benzene-1,2,3-tricarboxylic acid anhydride,butane-1,2,3,4-tetracarboxylic acid dianhydride, pyromellitic aciddianhydride, diphenyl-3,3',4,4'-tetracarboxylic acid dianhydride,naphthalene-2,3,6,7-tetracarboxylic acid dianhydride,naphthelene-1,4,5,8-tetracarboxylic acid dianhydride,diphenylether-3,3',4,4'-tetracarboxylic acid dianhydride,diphenylsulfone-3,3',4,4'-tetracarboxylic acid dianhydride,diphenylketone-3,3',4,4'-tetracarboxylic acid dianhydride,2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,furan-2,3,4,5-tetracarboxylic acid dianhydride andpyridine-2,3,5,6-tetracarboxylic acid dianhydride.

As the alkali metal fluoride useful in the practice of the process ofthe present invention may be mentioned, for example, lithium fluoride,sodium fluoride, potassium fluoride, cesium fluoride and rubidiumfluoride. In particular, potassium fluoride and rubidium fluoride arepreferred.

Further, the aforesaid alkali metal fluorides may be used in combinationwith a quaternary onium salt represented by the following formula:##STR1## wherein Z represents nitrogen (N) or phosphorus (P), R₁, R₂, R₃and R₄ represent an alkyl, cycloalkyl, aralkyl or aryl group, oradjacent two groups of R₁, R₂, R₃ and R₄ construct a structure ofheterocyclic compound with the central atom Z or further with otherhetero atoms, and X represents a halogen atom, a nitrile or hydroxylgroup in the process of the present invention.

The quaternary onium salt will be described in more detail as follows:the alkyl group represented by R₁, R₂, R₃ and R₄ may include C₁ -C₁₈alkyl groups such as methyl, ethyl, propyl, butyl, heptyl, hexyl,dodecyl and octadodecyl groups; the cycloalkyl group may include C₁ -C₄alkyl-substituted cyclopentyl and cyclohexyl groups; the aralkyl groupmay include C₁ -C₄ alkyl-, methoxy- or halogen-substituted benzylgroups; and the aryl group may include C₁ -C₄ alkyl-, C₁ -C₁₂ alkoxy- orhalogen-substituted phenyl groups; a heterocyclic structure constructedwith adjacent two groups of R₁, R₂, R₃ and R₄ and the central atom Z orfurther other hetero atoms such as O, S and N may include penta orhexa-heterocyclic structure, for example, pyrrolidine, piperidine andmorpholine ring. As illustrative examples of the quaternary onium saltmay be mentioned triphenylbenzylphosphoniumbromide,n-hexadecyltributylphosphoniumbromide, tetrabutylphosphoniumchloride,tetramethylphosphoniumhydroxide, tetraethylammonium chloride,tetraethylammoniumbromide, tetrabutylammoniumchloride,tetrabutylammoniumbromide, triethylbenzylammoniumchloride,cyclohexyloctyl dimethylammonium chloride, methylbutylpiperidiniumiodide, tetraethylammoniumcyanide, benzyltrimethylammoniumcyanide,benzyltrimethylammoniumhydroxide.

The heat resistant polymers obtained from organic polyisocyanates andorganic polycarboxylic acids or organic polycarboxylic acid anhydridesmay be divided roughly as (1) those from organic polyisocyanates andorganic polycarboxylic acids, (2) those from organic polyisocyanates andorganic polycarboxylic acids & organic polycarboxylic acid anhydrides,and (3) those from organic polyisocyanates and organic polycarboxylicacid anhydrides, all of which are useful as heat-resistant polymers. Thepolymers according to (1) has a structure comprising amido groups; thepolymers of (2) has a structure comprising amido groups and imidogroups; and the polymers of (3) has a structure comprising imido groups.

The reaction according to the process of the present invention iseffected by heating a mixture of an organic polyisocyanate, an organicpolycarboxylic acid or organic polycarboxylic acid anhydride and analkali metal fluoride or an alkali metal fluoride combined with aquaternary onium salt at a temperature of 20°-250° C. or preferably100°-200° C. for 1-20 hours in an inert organic solvent in asubstantially anhydrous state under the atmosphere of an inert gas suchas nitrogen. The molar ratio of the organic polyisocyanate to theorganic polycarboxylic acid or organic polycarboxylic acid anhydride tobe used in the reaction should be in the range of 0.70-1.30, with therange of 0.95-1.10 being particularly preferred. Any ratios outside thisrange will fail to produce heat-resistant polymers of high molecularweight.

The total amount of the alkali metal fluoride or alkali metal fluoridecombined with the quaternary onium salt to be used as the catalyst maypreferably be in the range of 0.01-10 mole % relative to the totalamount of the starting carboxylic acid or acid anhydride, with the rangeof 0.1-5 mole % being particularly preferred. Any amounts below thisrange will hardly produce polymers of high molecular weight, while anyamounts in excess of this range will bring about problems of qualitydegradation, for example, deterioration of heat-resistance of polymersdue to the catalyst residue remaining in the resultant polymers.Further, the amount of the quaternary onium salt to be used should be inthe range of 1-500 mole %, preferably of 10-300 mole %, or morepreferably of 30-200 mole % relative to the alkali metal fluoride.

The raw materials, i.e., the isocyanate and the carboxylic acid or acidanhydride and the catalyst, i.e., the alkali metal fluoride or alkalimetal fluoride with the quaternary onium salt may be fed to the reactionsystem either simultaneously or in an arbitrary order. Usually, they maybe fed thereto simultaneously at room temperature, optionally afterdissolving the raw materials in a solvent in advance. In some cases, itis possible to add either one of the raw materials, i.e., the isocyanateor the carboxylic acid or acid anhydride, or preferably the isocyanatecontinuously to the reaction system at a given reaction temperature. Theamount of the solvent to be used can be selected properly depending onthe property of the final polymers and the reaction temperature. Ingeneral, it is preferable to choose such conditions as not to cause anysubstantial hindrance to the stirring due to increased viscosity in thecourse of the polymerization.

Useful organic solvents in the practice of the process of the presentinvention may include, for example, linear or cyclic amides orphosphorylamides such as N,N-dimethylacetamide, N,N-dimethylformamide,N-methylpyrolidone, γ-butyrolactone and hexamethylphosphoric acidtriamide, sulfoxides or sulfones such as dimethylsulfoxide,diphenylsulfone and tetramethylenesulfone, ureas such as tetramethylureaand N,N'-dimethylethyleneurea, benzene, toluene, xylene, decalin,cyclohexane, heptane, hexane, pentane, methylene chloride,chlorobenzene, dichlorobenzene and tetrahydrofuran.

After completion of the polymerization, the polymer is separated assolid by introducing the reaction liquid into a non-solvent of thepolymer thereby causing the polymer to precipitate. The polymerthus-precipitated is then washed well with a similar non-solvent toremove the remaining solvent and other impurities. After the washing,the polymer is dryed at room temperature or at a high temperature,optionally under a reduced pressure. The resulting polymer may besubjected to melt molding, or in some cases, it may be re-dissolved in asolvent so as to be used as a vanish or adhesive or to produce a castfilm and fiber. Further, the polymer solution itself may also be used asa spinning dope.

The process of the present invention will hereinunder be illustrated bythe following examples. It should however be born in mind that thepresent invention is not limited by the following examples.

EXAMPLE 1

Charged in a 500-ml separable flask fitted with a stirrer, thermometer,condenser, dropping funnel and nitrogen inlet tube were 15.03 g (0.0905mole) of terephthalic acid, 15.07 g (0.0907 mole) of isophthalic acid,0.105 g (1.8×10⁻³ mole) of potassium fluoride and 412 ml oftetramethylenesulfone as a solvent. The resulting mixture was heated to200° C., added dropwise with 31.72 g (0.1821 mole) oftolylene-2,4-diisocyanate over 2 hours, stirred further for additional 2hours and allowed to cool down to room temperature. The mixture began tocause a polymer to precipitate in the course of the cooling and wasturned into a substantial slurry at room temperature. The solid in theslurry was washed well with a large amount of methanol and dryed at 150°C. under a reduced pressure for 3 hours.

The logarithmic viscosity (inherent viscosity (η_(inh)) measured at aconcentration of 0.1 g polymer/100 ml solvent and at a temperature of30° C. using concentrated sulfuric acid as the solvent; the same shallapply hereunder) of the resulting polymer was 3.0. IR spectrum of thepolymer revealed amido absorptions at 1,660 cm⁻¹ and 1,530 cm⁻¹.

A dope formed by dissolving the polymer in dimethylacetamide (10 wt. %)was cast on a glass plate and dryed at 50° C. under a reduced pressurefor one hour. The film thus-formed was peeled off from the glass plate,fixed in a frame and dryed at 280° C. under a reduced pressure for 3hours to obtain a tough, transparent, milky-white film. The tensilestrength of the film was 1,210 kg/m² and its elongation was 15%. The Tg(glass transition temperature) of the film was 265° C. (according to theTMA method). The 5 wt. %-reduction temperature measured with athermobalance (10 mg of sample were measured at a temperature increaserate of 10° C./min. in air) was 410° C.

EXAMPLE 2

Polymerization was carried out in the same manner as in Example 1 exceptthat cesium fluoride was used in place of potassium fluoride.Post-treatment was conducted in the same manner as in Example 1 toobtain a milky-white polymer powder. The logarithmic viscosity of thepolymer was 2.7, while the Tg of the film was 261° C.

COMPARATIVE EXAMPLE 1

Polymerization was carried out in the same manner as in Examples 1 and 2except for the exclusion of the fluoride compound as a catalyst.

A mixture of 15.10 g (0.0909 mole) of terephthalic acid), 14.97 g(0.0901 mole) of isophthalic acid and 410 ml of anhydrous sulfolane washeated to 200° C., at which temperature 31.52 g (0.1810 mole) oftolylene-2,4-diisocyanate was added thereto dropwise over 2 hours. Thereaction mixture was stirred further for additional 2 hours andthereafter allowed to cool down to room temperature. The polymersolution was emulsified in the course of the cooling and turned into asuspension at room temperature. The resulting suspension was introducedinto a large amount of methanol, and the product was filtered, washedwell with methanol and dryed at 150° C. under a reduced pressure for 3hours. The polymer thus-obtained was a white fine powder which was alow-molecular polymer with a logarithmic viscosity of 0.33.

COMPARATIVE EXAMPLE 2

Polymerization was effected in the same manner as in Examples 1 and 2,using sodium methoxide in place of the fluoride compound as thecatalyst.

A mixture of 14.96 g (0.0900 mole) of terephthalic acid, 15.11 g (0.0910mole) of isophthalic acid, 0.0980 g (0.0018 mole) of sodium methoxideand 410 ml of anhydrous sulfolane was maintained at 200° C., at whichtemperature 31.57 g (0.1813 mole) of tolylene2,4-diisocyanate was addedthereto dropwise over 2 hours. After stirring for additional 2 hours,the mixture was allowed to cool down to room temperature and treated inthe same manner as in Example 1 to obtain polyamide. The logarithmicviscosity of the polymer thus-obtained was 1.2. The Tg of the cast filmprepared in the same manner as in Example 1 was 261° C., while the 5 wt.%-reduction temperature measured with a thermobalance was 390° C. Thetensile strength was 950 kg/cm² and the elongation was 5%. These resultswere considerably inferior to those of the polyamide obtained in Example1.

EXAMPLE 3

Polycondensation of polyamide-imide was carried out using a similarapparatus to that employed in Example 1. Charged in the apparatus were20.05 g (0.1044 mole) of trimellitic acid anhydride, 0.0606 g (1.04×10⁻³mole) of potassium fluoride and 300 ml of N,N'-dimethylethyleneurea andthe resulting mixture was heated to 200° C. under stirring. To themixture maintained at this temperature was added dropwise a solutionformed by dissolving 26.26 g (0.1049 mole) ofdiphenylmethane-4,4'-diisocyanate in 50 ml of N,N'-dimethylethyleneureaover 4 hours. After proceeding with the reaction for additional 2 hours,the mixture was allowed to cool down to room temperature. The resultingmixture was introduced into a great quantity of methanol to allow apolymer to precipitate. The polymer was filtered, washed well with alarge quantity of methanol and dryed at 150° C. under a reduced pressurefor 3 hours.

The logarithmic viscosity of the resulting polymer was 1.12. IR spectrumof the polymer revealed imido group-based absorptions at 1,770 cm⁻¹ and1,720 cm⁻¹ and amido group-based absorptions at 1,660 cm⁻¹ and 1,530cm⁻¹.

The cast film prepared in the same manner as in Example 1 from asolution formed by dissolving the polymer in N-methylpyrolidone (10 wt.%) was a tough, light yellowish-green film with a tensile strength of1,290 kg/cm², an elongation of 28% and a Tg of film of 262° C. The 5 wt.%-reduction temperature of the polymer was 465° C. according to themeasurement with a thermobalance.

COMPARATIVE EXAMPLE 3

Polymerization of polyamide-imide was carried out in the same manner asin Example 3 except for the exclusion of potassium fluoride.

Charged in the flask were 20.01 g (0.1042 mole) of trimellitic acidanhydride and 250 ml of N,N'-dimethylethyleneurea and the resultingmixture was maintained at 200° C. A solution formed by dissolving 26.08g (0.1042 mole) of diphenylmethane-4,4'-diisocyanate in 50 ml ofN,N'-dimethylethyleneurea was added thereto dropwise over 4 hours. Afterproceeding with the reaction for additional 2 hours, the reactionmixture was allowed to cool down to room temperature. The resultingmixture was introduced into a great deal of methanol to allow a polymerto precipitate. The polymer was filtered, washed well with a largeamount of methanol and dryed at 150° C. under a reduced pressure for 3hours.

The polymer thus-obtained was identified from IR spectrum to bepolyamide-imide, which had a logarithmic viscosity of 0.23 and thus wasof extremely low molecular weight. A solution containing the polymerdissolved in N-methylpyrolidone was cast on a glass plate, dryed at 50°C. under a reduced pressure for one hour, increased in temperature to300° C. under the reduced pressure, and dryed at 300° C. under thereduced pressure for one hour to obtain a brownish transparent film. Thefilm had a tensile strength of 390 kg/cm² and an elongation of 1.0% andthus was very brittle.

EXAMPLE 4

Polymerization of polyimide was carried out in a similar apparatus tothat used in Example 1. Charged in the apparatus were 25.09 g (0.0779mole) of benzophenone-3,3',4,4'-tetracarboxylic acid dianhydride, 0.0592g (3.9×10⁻⁴ mole) of cesium fluoride and 250 ml ofN,N'-dimethylethyleneurea and the resulting mixture was maintained at200° C. A solution containing 19.65 g (0.0779 mole) ofdiphenylether-4,4'-diisocyanate dissolved in 50 ml ofN,N'-dimethylethyleneurea was added thereto dropwise over 2 hours,thereby causing a reaction. After proceeding with the reaction foradditional 2 hours, the reaction mixture was allowed to cool down toroom temperature. A portion of this polymer solution was introduced intoa great deal of methanol to cause a polymer to coagulate. Aftersufficient washing, the polymer was dryed at 150° C. under a reducedpressure for 3 hours to obtain a light yellowish powder of polyimide.The logarithmic viscosity of the polyimide was 1.24. Further, a portionof the polymer solution was cast on a glass plate and dryed in the samemanner as in Example 1 to obtain a tough, transparent, light brownishfilm. The film had a tensile strength of 1,170 kg/cm² and an elongationof 53%.

COMPARATIVE EXAMPLE 4

Polymerization of polyimide was carried out in the same manner as inExample 4 except for the exclusion of cesium fluoride. To a mixture of24.97 g (0.0775 mole) of benzophenone-3,3',4,4'-tetracarboxylic aciddianhydride and 250 ml of N,N'-dimethylethyleneurea maintained at 200°C. was added dropwise a solution containing 19.54 g (0.0775 mole) ofdiphenylether-4,4'-diisocyanate dissolved in 50 ml ofN,N'-dimethylethyleneurea over 2 hours. After proceeding with thereaction for additional 2 hours, the reaction mixture was treated in thesame manner as in Example 4 to obtain polyimide. This polymer had alogarithmic viscosity of 0.32 and thus was of very low molecular weight.Further, the polymer solution was cast on a glass plate, dryed at 50° C.under a reduced pressure for one hour, increased in temperature to 300°C. under the reduced pressure and dryed. The dryed film was however poorin film formability and too brittle to stand bending.

EXAMPLE 5

In the same separable flask as that used in Example 1 were charged 20.03g (0.1206 mole) of terephthalic acid, 6.679 g (0.0402 mole) ofisophthalic acid, 0.0467 g (8.0×10⁻⁴ mole) of potassium fluoride, 0.3111g (8.0×10⁻⁴ mole) of triphenylbenzylphosphoniumchloride and 350 ml ofanhydrous sulfolane. The resulting mixture was heated to 200° C., atwhich temperature 28.14 g (0.1616 mole) of tolylene-2,4-diisocyanate wasadded thereto dropwise over 2 hours. After proceeding with stirring foradditional 2 hours, the reaction solution was allowed to cool down toroom temperature. The solution began to cause a polymer to deposit inthe course of the cooling and was turned into a substantial slurry atroom temperature. The polymer was filtered, washed well with a greatdeal of methanol and dryed at 150° C. under a reduced pressure for 3hours to obtain a milky-white polymer powder. The logarithmic viscosityof the polymer thus-obtained was 3.3. IR spectrum of the polymerrevealed amido absorptions at 1,661 cm⁻¹ and 1,530 cm⁻¹. The cast filmprepared in the same manner as in Example 1 from the aromatic polyamidewas transparent, milky-white and tough. Its tensile strength was 1,310kg/cm² while its elongation was 14%. The glass transition temperature,Tg, of the film was 273° C. (according to the TMA method). The 5 wt.%-reduction temperature measured with a thermobalance was 412° C.

COMPARATIVE EXAMPLE 5

Polymerization was carried out in the same manner as in Example 4 exceptfor the exclusion of the fluoride compound and the quaternaryphosphonium salt as a catalyst.

A mixture of 20.14 g (0.1212 mole) of terephthalic acid, 6.713 g (0.0404mole) of isophthalic acid and 350 ml of anhydrous sulfolane was heatedto 200° C., at which temperature 28.17 g (0.1618 mole) oftolylene-2,4-diisocyanate was added thereto dropwise over 2 hours. Afterproceeding with stirring for additional 2 hours, the reaction solutionwas allowed to cool down to room temperature. The polymer solution wasemulsified in the course of the cooling and turned into a suspension atroom temperature. The suspension was introduced into a great quantity ofmethanol, and the product was filtered, washed well with methanol anddryed at 150° C. under a reduced pressure for 3 hours. The polymerthus-obtained was a white fine powder. It was a low molecular polymerwith a logarithmic viscosity of 0.29.

COMPARATIVE EXAMPLE 6

Catalytic effects of the quaternary phosphonium salt alone wereexamined.

Polymerization of polyamide was effected using a similar apparatus tothat employed in Example 1.

A mixture of 20.09 g (0.1209 mole) of terephthalic acid, 6.812 g (0.0410mole) of isophthalic acid and 350 ml of anhydrous sulfolane was heatedto 200° C., at which temperature 28.20 g (0.1619 mole) oftolylene-2,4-diisocyanate was added thereto dropwise over 2 hours. Afterproceeding with stirring for additional 2 hours, the reaction mixturewas allowed to cool down to room temperature. The cooled mixture was anemulsion, which is then introduced into a large amount of methanol tocause the product to precipitate. The product was filtered, washed wellwith methanol and dryed at 150° C. under a reduced pressure for 3 hours.The resultant polymer was a fine white powder which was a low molecularpolymer with a logarithmic viscosity of 0.43.

EXAMPLE 6

Polymerization of polyamide was effected using a similar apparatus tothat employed in Example 1.

Charged in the apparatus were 18.06 g (0.1087 mole) of isophthalic acid,6.211 g (0.0526 mole) of succinic acid, 0.2450 g (1.6×10⁻³ mole) ofcesium fluoride, 0.6222 g (1.6×10⁻³ mole) oftriphenylbenzylphosphoniumchloride and 350 ml ofN,N'-dimethylethyleneurea. The mixture was heated to 200° C., at whichtemperature 28.09 g (0.1613 mole) of tolylene-2,4-diisocyanate was addedthereto dropwise over 2 hours. The reaction mixture was subjected to thereaction for additional 2 hours. After cooling to room temperature, aportion of the resulting polymer liquid was introduced into a greatamount of methanol, thereby causing the polymer to coagulate. Thepolymer was then washed well with methanol and dryed at 150° C. under areduced pressure for 3 hours to obtain a milky-white polymer powder. Thelogarithmic viscosity of the polyamide was 1.5, while the 5 wt.%-reduction temperature measured with a thermobalance was 391° C. The Tgof the film prepared in the same manner as in Example 1 was 232° C.

COMPARATIVE EXAMPLE 7

Polymerization of polyamide was effected using sodium methoxide in placeof cesium fluoride and triphenylbenzylphosphoniumchloride.

Charged in the apparatus were 17.89 g (0.1077 mole) of isophthalic acid,6.181 g (0.0523 mole) of succinic acid, 0.0864 g (1.6×10⁻³ mole) ofsodium methoxide and 350 ml of N,N'-dimethylethyleneurea. To the mixturemaintained at 200° C. was added dropwise 27.88 g (0.1601 mole) oftolylene-2,4-diisocyanate over 2 hours. The reaction mixture wassubjected to the reaction for additional 2 hours. The polymer solutionthus-obtained was treated in the same manner as in Example 6 to obtain apolyamide powder. The polyamide had a logarithmic viscosity of 0.29 andthus was of extremely low molecular weight. The press sheet with athickness of 0.5 mm, which had been prepared by heat-pressing the powderat 280° C. and 100 kg/cm² was too brittle to subject it to physicalproperty measurements.

EXAMPLE 7

Polymerization of polyamide-imide was effected using a similar apparatusto that employed in Example 1. Charged in the apparatus were 20.11 g(0.1047 mole) of trimellitic acid anhydride, 0.1580 g (0.0010 mole) ofcesium fluoride, 0.0930 g (2.0×10⁻⁴ mole) ofn-hexadecyltributylphosphoniumchloride and 350 ml of anhydroussulfolane. The mixture was heated to 200° C. with stirring undernitrogen atmosphere. To the mixture maintained at this temperature wasadded dropwise a solution containing 13.09 g (0.0523 mole) ofdiphenylmethane-4,4'-diisocyanate dissolved in 30 ml of anhydroussulfolane for 2 hours. After proceeding with the reaction for additionalone hour, a solution containing 9.126 g (0.0524 mole) oftolylene-2,4-diisocyanate dissolved in 20 ml of anhydrous sulfolane wasadded thereto dropwise over one hour. After proceeding further with thereaction for one hour, the reaction solution was cooled to roomtemperature. In the course of the cooling, the reaction solution startedcausing a polymer to deposit and clouding from about 150° C. and downand was turned into a slurry when cooled down to room temperature. Thesolid in the slurry was filtered, washed well with a large amount ofwater and then with methanol, and dryed at 150° C. under a reducedpressure for 3 hours. The logarithmic viscosity of the polymerthus-obtained was 1.33. IR spectrum of the polymer revealed imido-bondabsorptions at 1,780 cm⁻¹, 1,720 cm⁻¹ and 1,370 cm⁻¹ and amido-bondabsorptions at 1,670 cm⁻¹ and 1,530 cm⁻¹. The cast film prepared in thesame manner as in Example 1 from a solution containing the polymerdissolved in N-methylpyrolidone (10 wt. %) was a tough and lightyellowish-green film with a tensile strength of 1,170 kg/cm², anelongation of 17% and a Tg of film (according to the TMA method) of 283°C. Further, the 5 wt. %-reduction temperature measured with athermobalance was 448° C.

COMPARATIVE EXAMPLE 8

Polycondensation of polyamide-imide was effected in the same manner asin Example 7 except that cesium fluoride andn-hexadecyltributylphosphoniumchloride were not used. The raw materialsused were as follows: 20.08 g (0.1045 mole) of trimellitic acidanhydride, 13.09 g (0.0523 mole) of diphenylmethane-4,4'-diisocyanate,9.091 g (0.0522 mole) of tolylene-2,4-diisocyanate and 400 ml ofanhydrous sulfolane. The reaction solution was emulsified in the courseof cooling. A portion of the resultant reaction mixture was introducedinto a great amount of methanol to cause a polymer to coagulate. Thepolymer cake thus-obtained was then washed well with methanol and dryedat 150° C. under a reduced pressure for 3 hours to obtain a lightyellowish polymer. The logarithmic viscosity of the polymer was 0.24.

EXAMPLE 8

Polymerization of polyimide was effected using a similar apparatus tothat employed in Example 1.

Charged in the apparatus were 25.09 g (0.0779 mole) ofbenzophenonetetracarboxylic acid dianhydride, 0.0930 g (0.0016 mole) ofpotassium fluoride, 0.3467 g (0.0008 mole) oftriphenylbenzylphosphoniumbromide and 300 ml ofN,N'-dimethylethyleneurea. The mixture was heated to 200° C. withstirring under nitrogen atmosphere. To the mixture maintained at thistemperature was added dropwise a solution formed by dissolving 9.748 g(0.0390 mole) of diphenylmethane-4,4'-diisocyanate in 20 ml ofN,N'-dimethylethyleneurea over one hour. After proceeding with thereaction for additional one hour, a solution containing 6.775 g (0.0389mole) of tolylene-2,4-diisocyanate dissolved in 20 ml of anhydrousN,N'-dimethylethyleneurea was added thereto dropwise over one hour.After proceeding further with the reaction for one hour, the reactionmixture was allowed to cool down to room temperature. The resultingreaction mixture was introduced into one liter of water under vigorousstirring. The precipitate thus-formed was filtered, washed well withwater and then with methanol, and dryed at 150° C. under a reducedpressure for 3 hours to obtain a light yellowish powder. The logarithmicviscosity of the polymer was 0.98. The tensile strength of the filmprepared in the same manner as in Example 1 from a solution containingthe polymer dissolved in N-methylpyrolidone was 1,090 kg/cm² and itselongation was 27%. The 5 wt. %-reduction temperature of the polymermeasured with a thermobalance was 480° C.

COMPARATIVE EXAMPLE 9

Polymerization of polyamide-imide was effected in the same manner as inExample 8 except for the exclusion of potassium fluoride. The rawmaterials used were as follows: 24.97 g (0.0775 mole) ofbenzophenonetetracarboxylic acid dianhydride, 0.3111 g (8.0×10⁻⁴ mole)of triphenylbenzylphosphoniumbromide, 9.685 g (0.0387 mole) ofdiphenylmethane-4,4'-diisocyanate, 6.757 g (0.0388 mole) oftolylene-2,4-diisocyanate, and 340 ml of anhydrousN,N'-dimethylethyleneurea. The polymer prepared by undergoing the samepost-treatment as in Example 8 had a logarithmic viscosity of 0.29.

EXAMPLE 9

Polymerization of polyimide was effected using a similar apparatus tothat employed in Example 1.

Charged in the apparatus were 20.15 g (0.1017 mole) ofbutanetetracarboxylic acid dianhydride, 0.1772 g (0.0030 mole) ofpotassium fluoride, 0.4316 g (0.0010 mole) oftriphenylbenzylphosphoniumbromide and 350 ml ofN,N'-dimethylethyleneurea. The mixture was heated to 200° C. undernitrogen atmosphere. To the mixture maintained at this temperature wasadded dropwise a solution formed by dissolving 17.73 g (0.1018 mole) ofdiphenylmethane-4,4'-diisocyanate in 50 ml of N,N'-dimethylethyleneureaover 2 hours. After proceeding with the reaction for additional 2 hours,the reaction mixture was allowed to cool down to room temperature. Thereaction mixture was then introduced into one liter of water undervigorous stirring. The polymer thus-deposited was filtered, washed witha large quantity of water, and dryed at 150° C. under a reduced pressurefor 3 hours to obtain a light yellowish powder. The logarithmicviscosity of the polyimide was 1.14 and the cast film prepared in thesame manner as in Example 1 was tough and had a tensile strength of 890kg/cm² and an elongation of 35%.

What is claimed is:
 1. A process for preparing a heat-resistant polymerwhich comprises reacting an organic polyisocyanate with one or morecompounds selected from the group consisting of organic polycarboxylicacids and organic polycarboxylic acid anhydrides in the presence of analkali metal fluoride as a catalyst.
 2. A process as claimed in claim 1,wherein the heat-resistant polymer is prepared by reacting an organicdiisocyanate with an organic dicarboxylic acid.
 3. A process as claimedin claim 1, wherein the heat-resistant polymer is prepared by reactingan organic diisocyanate with a compound selected from the groupconsisting of organic tricarboxylic acids and tricarboxylic acidanhydrides.
 4. A process as claimed in claim 1, wherein theheat-resistant polymer is prepared by reacting an organic diisocyanatewith a compound selected from the group consisting of organictetracarboxylic acids and tetracarboxylic acid dianhydrides.
 5. Aprocess as claimed in claim 1, wherein the alkali metal fluoride ispotassium fluoride or cesium fluoride.